The ablation of fused silica and sapphire is investigated from the perspective of laser micromachining. In this study, dielectric rods are machined using a 12 ps pulsed laser at 1064 nm wavelength. The machining of the rods is a calibration method to determine process parameters for an analytical ablation model. More specifically, the ablation threshold fluence and effective penetration depth are determined under process-relevant conditions due to the removal of macroscopic volumes, which leads to a higher accordance. The introduced ablation model predicts macroscopic ablation volumes and ablation efficiencies of dielectric materials as a function of the angle of incidence. Originally, the ablation process model was developed for metals under the normal incidence, but this work extends its applicability to dielectrics. In contrast to metals, the optical penetration depth should be independent of the angle of incidence. Altogether, the presented model is universally applicable and can be seen as a first step toward computer-aided 3D-manufacturing using ultrashort pulsed lasers. The ability to predict ablation volumes and machine heat-sensitive tool materials with high accuracy and precision is demonstrated by the fabrication of end mills made of fused silica and sapphire with a diameter of 1 mm. This shows that picosecond lasers are well suited for the fabrication of such microcutting tools. In particular, the ability of ultrashort pulses to ablate materials independent of their hardness and without any wear makes this technology highly promising for the tooling industry.

When producing fiber-reinforced plastic (FRP) suitable for mass production, new technologies have to be developed to overcome existing challenges such as increased efficiency in resource consumption or higher process flexibility. In the past, laser processing has been shown to yield important advantages such as non-contact processing, no tool wear and high design flexibility.Pulsed laser ablation of FRP offers a promising alternative to state of the art mechanical blasting. The selective matrix removal enables a high potential to improve adhesive bonding, molding processes and coating deposition of lightweight materials, especially FRP-metal or FRP-ceramic hybrids. The resulting increase in surface area exhibits forms lock characteristics and simultaneously provides an expanded interface area. As a result, 40 % higher tensile strength can be reached in pull-off tests compared to a mechanically blasted organic sheet surface, joined by thermal spraying of aluminum on carbon fiber-reinforced epoxy (CFRP).

Silicon alumina nitride (SiAlON) and alumina toughened zirconia (ATZ) ceramics are applied for ceramic cutting tools to machine, e.g., cast iron, nickel base alloys and other difficult-to-machine materials. The state of the art technology for manufacturing of the cutting tool geometry is grinding. Laser processing of ceramics is already studied in terms of ablation rate and roughness evaluation with the application of dental implant manufacturing. In the present study, laser machining of the mentioned ceramics is explored with a laser beam source of 1064 nm wavelength and 10 ps pulse duration (FWHM). The angle dependent energy specific removal rate is described in a model and the optimal pulse fluence for the different materials and the irradiation angles can be derived. For processing at irradiation angle of up to 75° no decrease of the relative absorption could be observed. For ATZ, lowest surface roughness is determined for both, orthogonal and quasi-tangential processing angle. For SiAlON, the roughness decreases constantly for higher tilt angles. A significant difference in the material answer with change of the sample composition can be detected and the results show the potential of further developing SiAlON ceramics towards machineability for laser ablation.

No abstract

No abstract